The invention relates to a multifunctional device for injecting a fluid, in particular into the exhaust tract of an internal combustion engine.
It is known to inject aqueous urea solution (AdBlue®) into the exhaust tract of internal combustion engines, in particular diesel engines, in order to reduce the nitrogen oxides contained in the exhaust gases. If a delivery module provided for injecting the aqueous urea solution into the exhaust tract has a pump with a non-volumetric delivery action, a return line is required in order for excess amounts of urea solution delivered by the pump to be delivered from the pressure side of the pump back to the suction side, and for the injection pressure to be kept constant. A variable throttle is preferably provided in the return line such that the injection pressure can be adjusted by variation of the throttle cross section.
To remove air (bubbles) from the delivery module, it is necessary for the return line to be fully closed.
To make the delivery module resistant to ice pressure, it is known for a small amount of air to be sucked in through the injection opening in a pulsed manner, and for an air-filled compensation volume for the aqueous urea solution to thus be created in the delivery module. To trigger such a pulsed sucking-in process, the cross section of the controllable throttle which is arranged in the return line is enlarged very quickly (for example within approximately 40 ms) by a factor of more than 100.
The three described functions (pressure regulation, venting of the delivery module and sucking-in of air in order to improve resistance to ice pressure) may be realized by means of a 2/3 directional valve that has two ports and the stated three functions.
In addition to the stated three functions, there is often a requirement for the injection system to be fully evacuated. For this purpose, use is conventionally made of the pump that is provided for the injection of the fluid during normal operation. For this purpose, by means of an additional 4/2 directional valve, the pump is switched such that the inlet and outlet of said pump are interchanged, and the urea solution is sucked out of the delivery module, and delivered back into the tank, by operation of the pump.
In an injection system of said type, two switchable valves, a 2/3 directional valve and a 4/2 directional valve, are required in order to realize the desired four functions.